Resistance Random Access Memory, or “ReRAM,” is a non-volatile memory device employing reversible change in resistance in a thin film with application of electrical voltage bias across the film. Thus, data can be stored in a ReRAM cell by changing the resistance of the thin film, which can be a solid-state material. The thin film is referred to as a memory film or a read/write film. Examples of ReRAM devices are described in World Intellectual Property Organization (WIPO) Publication No. WO2007004843 A1 to Hong et al. and U.S. Patent Application Publication No. 2013/0043455 A1 to Bateman.
A resistive memory cell can be programmed into a set state having a low electrical resistance, or a reset state having a high resistance. A write operation stores data in a set of resistive memory cells by programming each resistive memory cell into a set state or a reset state depending on the contents of the data. For example, “1” can correspond to a set state and “0” can correspond to a reset state, or vice versa. The write operation is typically followed by a write verification operation that compares the data read from the data-containing resistive memory cells with the original data. A suitable sense margin is employed to ensure that each set state provides electrical current greater than a minimum set current under a read bias condition, and each reset state provides electrical current less than a maximum reset current that is less than the minimum set current under the read bias condition. Intermediate measured electrical current between the maximum reset current and the minimum set current is considered to be an indication of a failed memory cell, triggering marking of resistive memory cells providing such intermediate measured electrical current under the read bias condition as “bad” or “non-operational” cells. Such marking of cells as “bad” decreases the amount of total cells available for data storage.